We plan to continue with our investigations of the postnatal development of the nervous system and behavior in rats and cats under normal and experimental conditions. Morphological, physiological and behavioral techniques are utilized and the experimental treatments include undernutrition, ethanol administration, low-level X-irradiation, and experimental deprivation or enrichment. The parallel examination of the maturation of the cerebellar cortex and locomotion will be continued in order to gain a better insight into their interrelations and as a model of the vulnerability of a late-developing neurobehavioral system. We have recently expanded this project and begun to study the maturation of other components of the motor system: muscle, muscle spindle and myoneural junction, peripherally; spinal cord, and ascending and descending supraspinal mechanisms, centrally. The comparative maturation of the early-developing forelimbs and late-developing hindlimbs will be stressed. Another model structure that is being examined in a similar manner is the hippocampus. The morphological and physiological consequences of agenesis or paucity of granule cells are being determined. Behavioral studies are concerned with altered performance strategies (response emission or withholding, play, maternal-filial interaction) that can be related to "behavioral maturation". We recently succeeded in devising a procedure of feeding rats artificially from birth onward. This will allow us not only to better control schedules of undernutrition but also to raise young which are impoverished in sensory, motor and social experience. BIBLIOGRAPHIC REFERENCES: Altman, J., 1976. Experimental reorganization of the cerebellar cortex: V. Effects of early X-irradiation schedules that allow or prevent the acquisition of basket cells. J. Comp. Neur. 165: 31-48. Altman, J., 1976. Experimental reorganization of the cerebellar cortex: VI. Effects of X-irradiation schedules that allow or prevent cell acquisition after basket cells are formed. J. Comp. Neur., 165: 49-64.